Historically inorganic pigments, such as hydrated or anhydrous siliceous, metal silicates, sodium alumino silicates, hydrated aluminum silicates, e.g., clays, have found increasing uses in many industries. For example, such pigments are employed in paper coating compositions, as fillers for paper, paints, inks, etc., and as reinforcing pigments or fillers in elastomers and other polymeric materials. In addition to being used as fillers, inorganic pigments are often dyed or colored and used as color-imparting fillers in papers, paints, inks, etc. and as reinforcing pigments or fillers in elastomers and other polymetric materials.
In the process of dying or otherwise coloring pigments it is important to insolubilize or otherwise fix dyes onto the pigment particles. In this regard, it is often necessary to treat pigment particles in such a manner so as to improve the affinity of the pigment particles to the dyestuffs utilized.
Several methods of improving the affinity of various pigment particles to dyestuffs have been reported. U.S. Pat. No. 3,834,924 to Grillo teaches a process for manufacturing surface modified inorganic pigments. The process according to this patent includes adding amino organosilanes to an aqueous dispersion of an inorganic pigment whereby the inorganic pigment is contacted with the amino organo silane and reacts so that the surface of the inorganic pigment is modified in such a manner to increase the affinity for dyes.
U.S. Pat. No. 3,545,909 to Gagliardi teaches aminoalkyl silicone coloring assistances that may be applied in the form of a pre-treatment to condition inorganic pigment substrates for a subsequent coloring operation. This pre-treatment with the aminoalkyl silicone coloring assistance induces dyable sites onto normally non-affinitive materials so that they may accept conventional anionic type organic dye stuffs.
U.S. Pat. No. 4,084,983 to Bernhard et al teaches a process for producing colored lustrous pigments in which a firmly adhering coating of aluminum hydroxide is first applied to pigment substrates, the aluminum ions contained in the coating are then reacted in order to form a firmly adhering dyestuff layer. In this manner the substrate is coated with a starting material which is convertible into a colored layer.
U.S. Pat. No. 4,543,128 to Troesche et al teaches a process for dying inorganic pigments that can be used as fillers. According to this patent pigments are dyed with polycationic dyestuffs in a process that involves providing a colored composition of an aqueous paste for dispersion of the white pigment with a water-soluble polycationic dye stuff. An optional, conventional, fixing agent may be used in this process.
U.S. Pat. No. 4,566,908 to Nakatani et al teaches a process for producing an azoic pigment including a silica core with a coating of amino or polyazoic dye chemically bound to the surface of the silica core through an amino silane coupling agent.
While previous efforts had focused on various methods to fix diverse dyestuffs onto selective substrates, there is a long felt need for developing methods whereby safer organic dyes can be fixed onto pigment substrates and replace currently used cadmium and chromium red and yellow pigments which pose potential health problems both in the processing and use. In this regard, solvent dyes have been developed to overcome health concerns associated with cadmium and chromium red and yellow pigments in many rubber and plastics applications, however, solvent dyes are generally associated with disadvantages in that they are usually expensive, often hard to disperse, and sometimes degrade the rubber and plastic materials into which they are incorporated.
Water-soluble, organic dyes have the potential of addressing the problems of both inorganic pigments and solvent dyes in many applications. Nevertheless, methods for insolubilizing or fixing water-soluble, organic dyes, particularly dyes that can be used to replace currently used cadmium and chromium red and yellow pigments are lacking. The present invention provides a method for coloring pigment substrates which is an improvement over prior known methods.